Edge connectors are used to make electrical connections to printed or wired circuit boards. This is accomplished by spring contacts of the edge connector engaging contact elements on the circuit board. The board contact elements are conventionally parallel conductive traces extending from the edge of the circuit board. It is common practice to plate these conductive strips and the engaging parts of the spring contacts with precious metal, such as gold, to avoid contact oxidation problems. However, this conventional edge connector arrangement suffers from the following disadvantages:
(a) The cut edge of the circuit board at which the groups of board contact strips terminate, tends to bite into and scuff the precious metal plating on the spring contacts. Such scuffing occurs as the board contacts engage the ends of the contact strips. Any surface debris resulting from such scuffing tends to build up in front of the spring contacts as they slide over the board contact strips, which can adversely affect the electrical connections. Scuffing that removes the gold plating on the spring contact locations that engage the board contact strips, also degrades the connections.
(b) The contact strips on the circuit board tend to be unduly large and thereby occupy valuable board space which could be utilized for accommodating other circuit components. This feature is particularly important in the case of miniaturized circuit boards using surface mounting technology.
(c) The contact pressure (force per unit volume) between the spring contacts and the board contact elements tends to be undesirably low for optimum electrical connections between the contacts.
(d) It is difficult to determine when the connector spring contacts are fully engaged with the board contacts. This is largely due to the relatively high board insertion, especially for edge connectors having large numbers of spring contacts.
It has already been proposed in U.K. Patent No. 2179578B to replace the conventional contact strips along the edge of the printed circuit board with suitably positioned relatively small contact pads which are preferably dome-shaped. Such pads are attached to the board a short distance from its edge, to be engaged by the spring contacts of the edge connector. This contact arrangement overcomes some of the aforesaid disadvantages of the conventional edge connector. The present invention is directed to further improvements in the contact pad arrangement disclosed in the above-mentioned patent.